Hack and / - Lightning Hacks&mdash;the Command Next Door

Every year or so, I like to write a column I title “Lightning
Hacks”. This
column is inspired by the lightning talks you encounter at most conferences. In
a lightning talk, instead of having one speaker give a 60-minute
presentation, multiple speakers give short 5–10-minute presentations. By
the end of a lightning talk, you end up hearing about all sorts of cool
topics that wouldn't have gotten their own time slot. In this column, I
get a chance to talk about a few cool “hacks” I've run across that
by themselves wouldn't fill an entire column.

In past Lightning Hacks columns, I've covered a wide variety of different
topics, and in the previous edition, I focused strictly on hacks with
the ssh command. In this column, however, I showcase a few
interesting tricks with commands you might use every day. It's easy to
take your favorite programs for granted, but I've found that no matter
how long I use Linux, it seems I'm always picking up new time-saving
tips, and a Lightning Hacks column is as good as place as any to list a
few of my favorites.

New Ways to Escape

It isn't news to frequent readers of this column that I edit all of my
text files with vim. I've been using vim for so long, my muscle
memory for the Esc key is second nature. When you press the Esc key in
vim, you return back to the default navigation mode from whatever mode
you were in. When I'm at all unsure where I am or what mode I'm in, my
brain automatically has my hand bang on that Esc key like I'm a champion
Hungry Hungry Hippos player. Of course, on a modern
keyboard, the Esc
key is quite a way from home row, and what's worse, on some keyboards
(like on ThinkPads), the Esc key is in a different place, so someone like me hits
F1 half the time. It turns out, however, that Ctrl-[ functions just
like Esc in vim (and other programs that accept vi-style syntax, like
vimperator). Both of those keys are just a pinkie-reach away and keep
most of your fingers on home row. I have to say though, old habits die
hard. I had to put a post-it note on my monitor that read
“Ctrl-[” for
a few weeks before my fingers started to catch the hint. It takes
only a few weeks for the habit to form though, and before you know it, you'll
be shaving that extra millisecond off your typing time.

Now that I've removed yet another function from the poor Esc key, let's
give it something else to do. When I first set up my N900 with terminal
sessions, I ran into a problem a lot of portable computer users face:
half the special keys aren't on the tiny keyboard. In my case, this
presented quite a problem, because I am a heavy Irssi user and my keyboard
had no way to press Alt even in the special symbols menu. Without the Alt
key, it was a pain to switch between different Irssi windows. I wasn't
sure what to do until I discovered that in most terminal sessions, the
Esc key can substitute for Alt. It turned out my terminal emulator
had an Esc touchscreen key-mapped, so from that point on, I just pressed Esc
whenever I needed Alt. It also turns out this works the same way on all
of my laptop terminal sessions.

Open Vim to a Specific Line Number

This is a quick-and-simple tip that I can't believe took me so long
to discover. Quite often, you will be in a situation where you want
to open a file to a specific line number. A few good examples include
when you re-kickstart a server, go to ssh in to it and realize
the host keys have changed. The error message lists the line number with
the conflicting key, so it is easy to go in and erase it. Another common
example occurs when you are working on a script or configuration file
and see a reference to a syntax error on a specific line.

Back in the day, when I wanted to go to a specific line in vim, I would
open the file and press :<number><Enter> to go to the line, but if you want
to save a step, just add +<number> to the command line as an argument
when you execute vim. For instance, if I want to jump ahead to line
27 in my ~/.ssh/known_hosts file, I would type:

vim ~/.ssh/known_hosts +27

Filter Grep with Grep

Grep is one of the crucial tools you should master if you want to spend
any time on the command line. One of the most common ways I use grep
is to check whether a certain process is running and see its process
ID. For instance, if I want to check for the process ID of my cron
dæmon, I might type:

In this example, cron has a process ID of 1215. The annoying thing
though is that because I had cron in my grep command, it also showed up in
the output. This means every time I run this command, I have to be sure
to ignore that line in the output. Of course, I also could use grep to
filter itself:

That works; however, it's unnecessary. If I enclose one of the characters
in my first grep filter in brackets, it does the filtering for me:

$ ps -ef | grep [c]ron
root 1215 1 0 Feb23 ? 00:00:00 cron

This works because when I enclose c in brackets, it turns it into a
character class that contains only one character, c. However, the grep
command itself shows up in the process list with those brackets, so it
doesn't match my [c]ron pattern anymore.

Kyle Rankin is senior security and infrastructure architect, the author of
many books including Linux Hardening in Hostile Networks, DevOps Troubleshooting and The Official Ubuntu
Server Book, and a columnist for Linux Journal. Follow him @kylerankin